1. Field of the Invention
The present invention relates to a printing plate stacking device which stacks photosensitive lithographic printing plates.
Moreover, the present invention relates to a method of judging the authenticity of a state of detecting sheet members, which judges the authenticity of the detecting state of a sheet member detecting sensor. This method is applied to an operation controlling device which is equipped with a sheet member detecting sensor which detects the leading end portion of a sheet member while the sheet member is being conveyed, and which uses the detection of the leading end portion of the sheet member by the sheet member detecting sensor as a trigger for setting the timing of the operation of a subsequent process.
2. Description of the Related Art
Photosensitive lithographic printing plates, in which a photosensitive layer is formed on a support made of aluminum or the like, are a type of photosensitive material used for printing. Photosensitive lithographic printing plates will hereinafter be called “printing plates”. After being subjected to image exposure, the printing plate undergoes developing processing. The developing processing includes the respective processings of developing, rinsing, desensitizing, and drying. At the time of developing processing, the printing plates, which have been subjected to developing processing and discharged from the automatic developer, are successively stacked by a stacking device. A large number of the stacked printing plates are conveyed to the subsequent process.
Some stacking devices used in stacking printing plates are formed in a substantial V-shape as seen from the side, by a slope portion, which is inclined downwardly from the discharge opening of the automatic developer, and a stock portion, which opposes the slope portion. In such a stacking device, after a printing plate discharged from the discharge opening has been loaded on the slope portion, the slope portion is swung toward the stock portion around the lower end portion of the slope portion. The printing is thereby pivoted over and leaned up against the stock portion.
When a printing plate which has been discharged from the automatic developer is loaded on the slope portion, if the printing plate slides down the slope, when the bottom end of the printing plate abuts a stopper or the like and is stopped thereat, the bottom end portion of the printing plate may be damaged, such as may be broken or bent or the like.
Thus, there are stacking devices in which a sensor for plate detection is provided at the upper end portion of the slope portion in a vicinity of the discharge opening of the automatic developer, and a bracket, which moves downward while supporting the leading end of the printing plate, is provided along the top surface of the slope portion. In such a stacking device, when the leading end of a printing plate which is discharged out from the discharge opening of the automatic developer is detected by the plate detecting sensor, at the time when the leading end of the printing plate reaches the bracket, the bracket is moved downward in accordance with the conveying speed of the printing plate discharged from the automatic developer. Damage to the printing plate occurring when the printing plate, which is moving downward on the slope portion, stops, can thereby be prevented.
There are various sizes of printing plates having different lengthwise and widthwise dimensions. For example, in an automatic developer which subjects such printing plates to developing processing, printing plates having different widthwise dimensions and printing plates having different dimensions along the conveying direction thereof can be processed.
The stacking device is generally of a size corresponding to the largest sized printing plate. Thus, when stacking mainly small-sized printing plates, and in particular, printing plates whose dimension along the conveying direction is small, the space required for placement of the stacking device is overly large as compared with the size of the printing plates.
When the leading end of a printing plate, which is moving downward on the slope, is stopped by abutting a receiving plate provided at the stock portion, the leading end of the printing plate slides down from on the slope to onto the receiving plate. In such a case, when the printing plate is stopped on the slope, an impact is applied to the leading end of the printing plate, and the printing plate may be damaged.
In order to prevent such a situation from occurring, there is a printing plate stacking device having the following structure. Hooks which support the leading end of the printing plate move downward along the slope. When, at the bottom end of the slope, the hooks are pulled-in downwardly from the top surface of the slope, the leading end of the printing plate is transferred over to the receiving plate at the stock portion. The impact applied to the leading end of the printing plate is thereby lessened.
However, in this device as well, there are cases in which the leading end of a printing plate, which is sliding down the slope next, enters in between the receiving plate and a printing plate which has been previously stacked and leaned up at the stock portion. Thus, when the printing plate is reversed and pivoted over onto the stock portion in a state in which the lower end of the printing plate is resting on the receiving plate of the stock portion, the leading end of the printing plate may slip in between the receiving plate and a printing plate which is already stacked, or the leading end of the printing plate may bend and be damaged such as be broken or become bent or the like.
Further, a rotating plate, which rotates toward another inclined surface (stacking wall) is provided at the slope of the stacking device. At the point in time when the entire printing plate is supported at the slope, the rotating plate is rotated, and the printing plate is transferred to the stacking wall. By repeating this operation, printing plates are leaned up against and stacked at the stacking wall.
A stopper, which receives and stops the leading end portion of the printing plate, is provided at the slope. The stacking device has a structure in which, after the stopper is disposed at the top portion of the slope, while the stopper supports the leading end portion of the printing plate (i.e., the bottom end portion of the printing plate when the printing plate is on the slope), the stopper is moved toward the bottom portion of the slope in accordance with the speed of discharging the printing plate. In this way, the impact to the leading end portion of the printing plate due to the printing plate sliding down on the slope can be mitigated.
Control is carried out such that the timing for driving the stopper and the timing for rotating the rotating plate are triggered by detection by a printing plate detecting sensor provided at the uppermost end of the slope.
A reflection-type photoelectric sensor equipped with a light-projecting portion and a light-receiving portion is used as the printing plate detecting sensor. When an object to be detected is at a position at a predetermined distance from the sensor, the light irradiated from the light-projecting portion is reflected by the object to be detected and received at the light-receiving portion. Here, the object to be detected may be a printing plate. It is possible to discriminate between detection and non-detection of an object to be detected due to the presence or absence of received light.
The printing plate detecting sensor is disposed at the uppermost end of the slope in a state in which it is flush with the printing plate supporting surface. The printing plate can be detected by passing by the printing plate detecting sensor. However, if a worker is working at the region where the printing plate passes by, his/her arm or hand or a printing plate or part which the worker is holding, which has entered into the region at which a printing plate can be detected by the printing plate detecting sensor, may be mistakenly judged to be a printing plate which is being discharged from the automatic developer, and operation of the stopper and the rotating plate may be started.
In order to avoid such a situation, the printing plate detecting sensor may be disposed so as to oppose the slope and so as to be directed toward the slope surface at a bracket formed in an arch-shape. However, with such a structure, the region above the slope surface becomes narrow, and a problem arises in that the maintenance workability thereat deteriorates. Further, in order to provide such a bracket, the number of parts is increased, and the wiring and the like for the printing plate detecting sensor become complex.